1. Technical Field
The embodiments herein generally relate to spinal fixation devices, and, more particularly, to devices for preventing slippage between hook and vertebrae and methods of preventing slippage using the same.
2. Description of the Related Art
A unilateral or bilateral stress fracture of the narrow bridge between the upper and lower pars interarticularis is a common cause of lower back pain in adolescent athletes. A variety of surgical treatments have been used, including posterior fusion and posterolateral fusion, to address symptomatic spondylolysis. Moreover, there are many known spinal conditions that require imposition and/or maintenance of corrective forces on the spine in order to return the spine to its normal condition. As a result, numerous devices have been developed for use in spinal fixation. One such type of spinal fixation device generally includes one or more spinal rods placed parallel to the spine with fixation devices, such as hooks, screws, or plates, interconnected between the spinal rods and selected portions of the spine. Spinal fixation devices are used to correct problems in the lumber and thoracic portions of the spine, and are often installed posterior to the spine on opposite sides of the spinous process and adjacent to the transverse process. Conventional spinal fixation devices include a spinal rod connected to the spine using a hook which engages a portion of vertebrae. It is necessary for such spinal fixation devices to secure the vertebrae within the hook in order to ensure that the spinal rod remains correctly in place both during and after surgery.
Typically, spinal fractures and scoliosis have been treated with the use of distraction rods, such as the type known as Harrington rods, having hooks for engagement with vertebrae above and below the damaged spinal section. In most instances such hooks are capable of rotation about the rod, and are maintained at the desired angular orientations merely by the frictional resistance of screws located above and below the hook. Such mechanisms are relatively insecure and under high axial load the hooks tend to swing on the rod, and thus become disengaged from the vertebrae. One solution to this problem is the so-called Moe rod which has a square cross section, to which a matching cross section is provided in the hook openings. In this alternative, however, when the rod is bent (as it often must be) extreme care must be taken to bend it in the desired plane relative to the plane of the hooks, since no rotational adjustment of the hooks on the rod is possible. Precise bending is often difficult to achieve.